Lip anatomy and its implications for the pollination mechanisms of Bulbophyllum species (Orchidaceae)

BACKGROUND AND AIMS: The lip structure of six Brazilian and one Asiatic species of Bulbophyllum with wind-assisted fly pollination (B. involutum, B. ipanemense and B. weddellii) and non-wind-assisted fly pollination (B. epiphytum, B. glutinosum, B. regnellii and B. rothschildianum) was studied to investigate the presence of secretory tissues related to these pollination mechanisms. METHODS: The lip study was carried out through scanning electron microscopy (lip surface) and light microscopy (anatomical features). KEY RESULTS: In most of the species studied, the osmophores (odour glands) were located in the lobes and in the upper surface of the lip callus. Differences in the lip structure were observed between the two groups (the presence of a nectary and the extent of osmophore surface), depending on the mechanism of pollination. Nectaries were found in the cavity callus in B. ipanemense, B. involutum and B. weddellii, even though their pollinators were presumably attracted by the instinct to oviposit. CONCLUSIONS: These findings corroborate the hypothesis that, because pollination in these species is dependent on an unpredictable external factor (wind), nectar is necessary to keep the insect in the flower for a long period. Despite the occurrence of a liquid-like nectar in the flowers of B. epiphytum, B. glutinosum, B. regnelli and B. rothschildianum, no anatomical evidence for nectaries was found in the lips of these species, although a similar structure may occur in another region of the flowers. This observation agrees with the fact that pollination by lip movement in the latter species requires only gravity, with no additional mechanism being needed to keep the flies in the flower.     

Rhythms of fragrance emission in flowers

A method for the sampling of volatiles emitted by individual flowers is described. Sampling over periods of 3 h allowed the examination of diurnal changes in quantity and quality of fragrance. In the species studied, Odontoglossum constrictum Lindl., Citrus medica L., Hoya carnosa R. Br., and Stephanotis floribunda Brongs., the fragrance was characterized by a few major components accompanied by a larger number of minor components. Flowers of all species produced volatiles in a rhythmical, diurnal fashion. Whereas in detached flowers of O. constrictum and C. medica rhythmicity could be observed for up to four cycles, flowers of H. carnosa showed this phenomenon only when attached to the plant. Maxima of emission were observed during the day in C. medica and O. constrictum whereas in H. carnosa it occurred during the night. In S. floribunda a conspicuous asynchronism of the emission of different volatiles was observed, resulting in the rhythmical change of fragrance quality.     

Influence of temperature on the rhythmic emission of volatiles from Ribes nigrum flowers in situ

The floral volatiles of blackcurrant (Ribes nigrum) were collected in situ using the headspace technique. Eleven compounds were identified, including monoterpenes hydrocarbons and monoterpene ethers. The fragrance was emitted in a rhythmic manner, the maximum being in the middle of the photoperiod. Emission at 20°C was significantly higher than at 10°C. The rhythmic nature of emission seemed to cease under conditions of constant light. However, a slight rise in emission during the second period in continuous light may indicate a circadian control of emission. The significance of flower volatiles in relation to pollination is discussed.     

'Floral' scent production by Puccinia rust fungi that mimic flowers

Crucifers (Brassicaceae) in 11 genera are often infected by rust fungi in the Puccinia monoica complex. Infection causes a 'pseudoflower' to form that is important for attracting insect visitors that sexually outcross the fungus. 'Pollinator' attraction is accomplished through visual floral mimicry, the presence of a nectar reward and floral fragrances. Here we used gas chromatography and mass spectrometry to identify and quantify fragrance production by these rust fungi on several Arabis hosts, and by co-occurring true flowers that share insect visitors. Fungal pseudoflowers produced distinctive floral fragrances composed primarily of aromatic alcohols, aldehydes and esters. Pseudoflower fragrances were chemically similar to noctuid-moth-pollinated flowers, such as Cestrum nocturnum and Abelia grandiflora , but were very different from host flowers, host vegetation and the flowers of coblooming, nonhost angiosperms. There was variation in the quantity and composition of fragrance profiles from different fungal species as well as within and among hosts. The evolution of scent chemistry is relatively conservative in these fungi and can be most parsimoniously explained in three steps by combining chemical data with a previously determined rDNA ITS sequence-based phylogeny. Pseudoflower scent does not appear to represent a simple modification of host floral or vegetative emissions, nor does it mimic the scent of coblooming flowers. Instead, we suspect that the unique fragrances, beyond their function as pollinator attractants, may be important in reducing gamete loss by reinforcing constancy among foraging insects.     

Novel reports of glands in Neotropical species of Indigofera L. (Leguminosae,Papilionoideae)

By considering controversial discussions in the literature with regard to gland denomination in Indigofera species, as well as the taxonomic value of secretory structures in Leguminosae, we aim to morphologically detail glands that had been previously observed in I. microcarpa and I. sabulicola, and to investigate the occurrence of glands in vegetative and reproductive organs of other six Neotropical species that belong to the genus. Glands analyzed through scanning electronic microscopy (SEM) in combination with anatomic analyses correspond to secretory trichomes that are classified into seven types. Main variations in relation to types occurred with regard to head shape and peduncle size. Trichome heads were multicellular, with a thin cuticle. Hollow heads with conspicuous inner space characterized only one type (type 1); the other trichome types had massive heads. Peduncles, which varied from biseriate to multiseriate, had thick, pecto-cellulosic cell walls. Trichomes were found on stems, stipules, petioles, rachis, petiolules, leaflets, bracteoles, sepals, standards and fruits, more commonly along the margins. Each of the eight Indigofera species analyzed had at least two different trichome types out of the seven types that occurred in reproductive and vegetative organs of these taxa. Various types of secretory trichomes were found in I. campestris, I. lespedezioides, I. microcarpa, I. spicata, I. suffruticosa and I. truxillensis. Stems and rachis were the vegetative organs in which a greater variety of trichomes occurred, and sepals were parts of reproductive organs with the same status. Five out of the seven secretory trichome types occurred on both vegetative and reproductive organs. Distribution and gland types differed between species and these gland distribution patterns can be used as diagnostic characters. Reports of glands in Indigofera campestris, I. hirsuta, I. lepedezioides, I. suffruticosa, I. spicata and I. truxillensis, their recognition as secretory trichomes, and the morphological variety of types found for such trichomes are novel data for Indigofera.     

Specialized use of pollen vectors by Caesalpinia gilliesii, a legume species with brush-type flowers

The pollination of Caesalpinia gilliesii (Fabaceae) , a legume species with long, brush-type flowers, was studied in wild populations in Argentina. A total of 341 hawkmoths (Sphingidae), belonging to 10 species, with tongues ranging from 1.5 to 13.5 cm in length, were captured by means of light traps. Hawkmoths could be classified in four significantly different tongue-length classes or guilds: short (15.35 ± 1.11 mm), medium (30.23 ± 2.24 mm), long (55.85 ± 4.98 mm) and very long (95.61 ± 13.63 mm). A total of 133 of the hawkmoths, belonging to seven species, carried pollen of Cae. gilliesii , mainly on their venter. Successful contact with anthers while drinking nectar depended upon hawkmoth tongue length. The relative frequency of pollen-carriage and the mean tongue length of each species were positively and significantly correlated. Considering a null hypothesis of nonspecialization, in which hawkmoths carrying pollen are distributed at random among individuals of the four guilds, long-tongued hawkmoths carried Cae. gilliesii pollen more frequently than would be expected by chance. In contrast, short- and medium-tongued guilds carried pollen less frequently than is predicted by random expectation. Individuals with short tongues accessed nectar from below without touching the anthers, whereas very long-tongued hawkmoths, with tongues longer than the length range of the flower reproductive organs, can probably reach nectar without touching the fertile organs. Results show that a pterotribic pattern of pollen deposition on the body of long-tongued hawkmoths is operating in this species. This suggests that brush-type blossoms are not necessarily unspecialized, despite popular belief.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 579–592.     

Integrating floral scent, pollination ecology and population genetics

1 . Floral scent is a key factor in the attraction of pollinators. Despite this, the role of floral scent in angiosperm speciation and evolution remains poorly understood. Modern population genetic approaches when combined with pollination ecology can open new opportunities for studying the evolutionary role of floral scent.
2 . A framework of six hypotheses for the application of population genetic tools to questions about the evolutionary role of floral scent is presented. When floral volatile chemistry is linked to pollinator attraction we can analyse questions such as: Does floral volatile composition reflect plant species boundaries? Can floral scent facilitate or suppress hybridization between taxa? Can the attraction of different pollinators influence plant mating systems and pollen-mediated gene flow? How is population genetic structure indirectly influenced by floral scent variation?
3 . The application of molecular tools in sexually deceptive orchids has confirmed that volatile composition reflects species boundaries, revealed the role of shared floral odour in enabling hybridization, confirmed that the sexual attraction mediated by floral odour has implications for pollen flow and population genetic structure and provided examples of pollinator-mediated selection on floral scent variation. Interdisciplinary studies to explore links between floral volatile variation, ecology and population genetics are rare in other plant groups.
4 . Ideal study systems for future floral scent research that incorporate population genetics will include closely related taxa that are morphologically similar, sympatric and co-flowering as well as groups that display wide variation in pollination mechanisms and floral volatiles.     

Further observations on rhythmic emission of fragrance in flowers

Observations regarding floral fragrance and the rhythmicity of its emission in four plant species are reported. In the case of flowers of Hoya carnosa R. Br. which are characterized by circadian rhythmicity of scentedness (R. Altenburger and P. Matile, 1988, Planta 174, 248–252), temperature compensation of the free-running period as well as persistence of oscillations in permanent darkness have been demonstrated. A hitherto unidentified component of fragrance turned out to be identical to an unusual sesquiterpene recently discovered in cardamom oil (B. Maurer et al., 1986, Tetrahedron Lett. 27, 2111–2112). In Stephanotis floribunda Brongs. the rhythmic emission of fragrance is circadian in nature, but in a constant environment the oscillations of individual components are increasingly asynchronous. In excised flowers of Odontoglossum constrictum Lindl. the diurnal oscillations observed in a natural photoperiod are abolished under constant environmental conditions. They are resumed upon the return to a 1212-h photoperiod. The absence of circadian control could also be demonstrated in excised flowers of Citrus medica L. In this species, too, the daily maxima of scent emission reappear upon the transfer of flowers to a 1212-h light/ dark cycle. Results obtained upon the comparative analysis of volatiles in the headspace above the flowers and in petal extract indicate that the relative abundance of an individual compound in the floral fragrance is not a function of differential volatility.Abbreviations DL 1212 h photoperiod - DD continuous darkness - GLC gas-liquid chromatography - LL continuous illumination The authors are indebted to R. Kaiser, Givaudon Corp.for kindly carrying out the identifikation of volatiles by gas-liquid chromalography/mass spectrometry.     

Presence of the anther gland is a key feature in pollination of the early‐branching papilionoids Dipteryx alata and Pterodon pubescens (Leguminosae)

• The presence of glandular appendages in the anthers is a rare condition in angiosperms. In Leguminosae it occurs in species of the Mimosoid clade and in early‐branching clades of papilionoids such as Dipterygeae. In Dipterygeae such appendages surprisingly exhibit a secretory cavity instead of secretory emergences as is the case for the Mimosoid clade. Thus, the objective of this study was to elucidate the function of anther glands in Dipteryx alata and Pterodon pubescens, species in the Dipterygeae clade that exhibit a pollen release mechanism that is intermediate between the explosive and valvular types.
• Flower buds and flowers were processed for surface, anatomical, histochemical and ultrastructural analyses.
• Anther glands consist of a cavity secreting sticky substances (oleoresins and polysaccharides) that play a key role during the flower's lifespan by aggregating pollen grains and attaching them to the floral visitor's body. Other floral features that are important for understanding the pollen release mechanism that is intermediate between the valvular and the explosive types are: (i) keel petals intertwined with tector trichomes; (ii) glandular appendages in the abaxial and lateral sepals and in petals composed of secretory ducts; and (iii) a continuous secretion process of the anther glands followed by an asynchronous dehiscence of anthers.
• The well‐adapted papilionoid flag blossom with anther glands and keel petals intertwined with trichomes provided the foundation for a successful canalisation toward a pollen release mechanism intermediate between the explosive and valvular types inside early‐branching papilionoids.

     

Flower Scent and Pollination in Selected Neotropical Palms

Abstract: The flower scents of 14 palm species were collected in the field in Ecuador and Puerto Rico by head-space adsorption and analysed by gas chromatography-mass spectrometry. Insect visitors were recorded in seven of the species in Ecuador. The floral scent of the different species was dominated by a variety of compounds, e.g., the fatty-acid derived 3-pentanone and the hydrocarbon series dodecane to pentadecane, the benzenoid compound 1,4-dimethoxybenzene, the isoprenoids ( E )-ocimene, myrcene, linalool, and ( E )-α-farnesene and the nitrogen-containing compound 2-methoxy- sec -butylpyrazine. Rather than mirroring the systematics of the studied palm species, the chemical composition of the floral scent reflected the pollination mode. The scent of beetle-pollinated species was characterized by large amounts of one or a few dominant compounds, whereas fly- and bee-pollinated species contained a mixture of several compounds in smaller total amounts. We suggest that specific scent compounds, as found in the beetle-pollinated species, have evolved as a response to pollinator preferences. The importance of olfactory cues in relation to visual cues is higher in beetle-pollinated species than in species pollinated by flies and bees.     

天南星科植物的花多样性与传粉策略

天南星科植物具有特殊的佛焰苞花序及多样化的传粉策略, 是研究被子植物花的分化与动植物之间进化生态学联系的理想材料。本文简述了天南星科不同类型的花序结构及其传粉适应意义, 总结了天南星科传粉策略的基本类型与演化历史。天南星科的苞片结构主要包括原始型、外展平面型、直立宽佛焰苞型和直立狭佛焰苞4种类型, 呈现出从简单的片状与外展平面状结构向复杂的立体包裹状的佛焰苞结构演化的趋势。肉穗花序可分为两性花花序、单性花雌雄同序和单性花雌雄异序3种类型, 演化路线为两性花花序→单性花雌雄同序→单性花雌雄异序。天南星科的传粉者主要有鞘翅目、双翅目、膜翅目昆虫, 表现出5种主要传粉策略: 食物报酬型互利传粉、气味吸引型欺骗性传粉、交配场所型互利传粉、产卵场所型互利传粉和致死陷阱型欺骗性传粉。天南星科植物通过花序的形状、颜色、产热以及花部挥发物来吸引传粉者, 其中最主要的挥发物有二甲基硫化物、甲基吲哚化合物、萜类和苯类化合物, 模拟食物或产卵场所信号吸引鞘翅目甲虫和双翅目昆虫为其传粉。天南星科植物的佛焰苞被认为是促进该科物种分化的一个重要结构, 但该性状的演化历史及其与传粉系统分化之间的内在联系尚不明确。利用现代分子生物学技术以及模型模拟等手段, 结合生理生态学方法深入探究传粉事件与天南星科植物的花多样性以及物种分化之间的联系, 有望提升关于植物-传粉者互作与植物的花多样性分化之间关系的认识, 并丰富对被子植物多样性演化相关研究的理解。     

Insecticidal amino acids in legume seeds

When incorporated into artificial diets, powdered seeds of several Central American legume species were found to be toxic or repellent to larvae of the southern armyworm. Similar results were obtained from bioassay experiments with certain unusual amino acid components of these seeds, suggesting that these compounds may contribute to the known resistance of many legume seeds to natural attack by insects.     

异型雄蕊植物花内雄蕊的分化

Flowers that have heteromorphic stamens （heterantherous flowers） have intrigued many researchers ever since the phenomenon was discovered in the 19th century. The morphological differentiation in androecia has been suggested as a reflection of ＂labor division＂ in pollination in which one type of stamens attracts pollinators and satisfies their demand for pollen as food and the other satisfies the plant＇s need for safe gamete dispersal. The extent and patterns of stamen differentiation differ notably among taxa with heterantherous flowers. Seven species with heteromorphic stamens in three genera were sampled from Leguminosae and Melastomataceae, and the morphological difference of androecia, pollen content, pollen histochemistry and viability, pollen micro- morphology, as well as the main pollinators were examined and compared. Pollen number differs significantly between stamen sets of the same flower in most species investigated, and a correlation of pollen number and anther size was substantiated. Higher pollen viabilities were found in the long （pollinating） stamens of Senna alata （L.） Roxb. and S. bicapsularis （L.） Roxb. Dimorphic pollen exine ornamentation is reported here for the first time in Fordiophytonfaberi Stapf. The height of stigma and anther tips of the long stamens in natural conditions was proved to be highly correlated, supporting the hypothesis that they contact similar areas of the pollinator＇s body.     

Morpho–anatomical and ultrastructural analysis of extrafloral nectaries in Inga edulis (Vell.) Mart. (Leguminosae)

The presence of extrafloral nectaries (EFNs) between leaflets is an usual feature in Inga edulis (Vell.) Mart. (Leguminosae). Extrafloral nectaries are secretory structures involved in production of nectar and which serve in the protection of plants against herbivores through association with ants. This study aimed to characterize the EFNs of I. edulis at different developmental stages and describe their morphology, histochemistry and ultrastructure. Leaf fragments, containing secretory structures, were processed according to standard methods for light, scanning and transmission electron microscopy. The EFNs were classified into three stages based on morphology: pre‐secretory, secretory and post‐secretory. The pre‐secretory stage occurs in young leaves, whereas secretory and post‐secretory stages occur in developed and senescent leaves, respectively. The EFNs possess a concave surface and a central cleft in which nectar is accumulated and which was not observed in pre‐secretory EFNs. Histochemical tests identified the presence of sugars, proteins, phenolic compounds, mucilage and lipids at all developmental stages of the EFNs. Calcium crystals were identified in all tissues and stages of the EFNs. The secretory cells of the EFNs exhibit a granular cytoplasm, small vacuoles, prominent nuclei, smooth endoplasmic reticulum and mitochondria. Post‐secretory stage EFNs exhibited intense cytoplasmic degradation and the presence of microorganisms. The performance of EFNs of I. edulis appear to follow the leaf development.     

Specialized pollination by spider-hunting wasps in the African orchid Disa sankeyi

Disa sankeyi Rolfe was found to be pollinated almost exclusively by Hemipepsis wasps (Pompilidae) at sites across its range in the Drakensberg mountains of South Africa. Wasps of both sexes appear to locate the cryptic yellow-green flowers primarily by using scent cues, as they show a classic zigzag flight pattern when approaching inflorescences. The sweet-spicy fragrance emitted by the flowers is strong enough to be discernable by a human from several metres away and consists of a blend of at least 65 volatile compounds, with (E)- cinnamic aldehyde and eugenol as the major constituents. On settling, wasps lick the exposed droplet of nectar that is secreted from the mouth of the reduced floral spur on each flower. Pollinaria become attached to the front feet of the wasps as they grasp flowers adjacent to those on which they are feeding. Pollen transfer to stigmas similarly takes place on flowers adjacent to those that are used as a nectar source. Almost 100% of flowers in the study populations were found to have been pollinated. Specialized pollination by pompilid wasps appears to be a rare phenomenon that has been reported only in southern African plant species. It appears to be associated with cryptic green-yellow flowers and highly accessible nectar. Behavioural assays are required to determine whether the basis of the specialization in this pollination system lies in a particular chemical composition of the floral fragrance.     

Rodent pollination in the Cape legume Liparia parva

Flowers of Liparia parva from which rodents were excluded had lower seed‐set than open flowers. The rodent Acomys subspinosus was captured in the vicinity of this plant species and captures had substantial numbers of L. parva pollen in their scats. Captured individuals of A. subspinosus visited L. parva flowers in tanks and removed standard petals to obtain the nectar. Typical of rodent‐pollinated species, L. parva, flowered in winter and flowers mostly opened in the evenings and the stigma‐nectar distance was about 10 mm. This is the first evidence for rodent pollination in the large cosmopolitan family, the Fabaceae.     

Anomalous secondary thickening in roots of Daviesia (Fabaceae) and its taxonomic significance

PATE, J. S. KUO, J., DIXON, K. W. & CRISP, M. D., 1988. Anomalous secondary thickening in roots of Daviesia (Fabaceae) and its taxonomic significance . Investigations of 55 species of Daviesia show 24 to have anomalous secondary vascular development in their roots and the remainder to be of conventional root anatomy. Species showing the trait exhibit early cessation of cambial activity in the central stele of the seedling followed by differentiation of a series of concentric layers of inter-connecting vascular strands, each layer derived from new cambial activity in pericycle tissue outside the existing vasculature. The ontogeny and mature structure of the anomalously thickened roots of certain species is described and the findings compared with published data for other genera of dicotyledons. A cladogram is presented to portray the phylogeny of the species of Daviesia included in the study, using 36 morphological features and the parsimony method to derive minimum length Wagner-type trees from a matrix of taxa character states. Evolution of the character of anomalous root thickening is concluded to have occurred early and possibly on two independent occasions during specialion of the genus.